The invention relates to methods of handling wind turbine blades and mounting said blades on a wind turbine, and a system and gripping unit for handling a wind turbine blade.
Modern wind turbines usually comprise a rotor with a considerable diameter and weight, as illustrated in FIG. 1. The diameter of modern rotors is approaching 100 to 150 meters and the rotor including the wind turbine hub and e.g. three wind turbine blades may add up to around 40 to 50 tons.
The usual way of mounting a wind turbine includes the steps of transporting the different elements to the site of the wind turbine, assembling the tower sections and the tower, lifting the wind turbine nacelle with a crane and mounting the nacelle on top of the tower, assembling the wind turbine rotor on the ground, and lifting the wind turbine rotor with the crane and mounting the rotor to the low speed shaft extending from the nacelle.
The usual way comprises a number of disadvantages which have become more and more problematic with the increasing size and weight of the wind turbine rotor.
Especially assembly of the wind turbine rotor on the ground is problematic as it requires a large area free of obstacles, which is planar and stable in order to be accessible for the assembly workers and the crane. With a rotor diameter of 100 meters, the area in question must exceed 5000 m2.
Further, lifting of the rotor to the nacelle is rather complicated, as the rotor must be turned 90 degrees in midair.
In other lifting systems, it is known to pre-mount the wind turbine hub on the nacelle and then lift each wind turbine blade successively to a position next to hub and perform the mounting of the blades. The lifting is performed with the wind turbine blades lying in a number of slings.
This lifting system comprises a number of disadvantages and one of them is the fact that the blade has to be horizontal during lifting and mounting.
Further, the blade has to be positioned with the front facing downwards to the bottom of the slings in order not to be damaged. This only allows mounting of the blade on the hub in a production position which means that the hydraulic pitch system of the wind turbine has to be manually overruled and mechanical break force to be added to the low-speed axle of the turbine in order to keep the rotor system from rotating during mounting.